The present invention relates to a new intravascular apparatus and method that can be used as a therapy for diseases of the vascular system that are characterized by an undesired obstruction or restriction of a vascular segment, or that can be used in conjunction with other intravascular therapeutic or diagnostic apparatuses or methods. More particularly, the present invention relates to a new intravascular apparatus and method for recanalization of an obstructed vessel or for removal and/or reduction of undesired material that obstructs or occludes a vessel by application of low frequency mechanical energy to a vessel site or by creation of cavitation at the vessel site.
Obstructive arterial disease continues to be serious health problem in our society today. Obstructive arterial disease can occur in coronary or peripheral arteries. This disease is the result of the deposit and accretion of fatty substances on the interior surface of the walls of the arteries. The build up of such deposits results in a narrowing of the diameter of the artery which restricts the blood flow through the artery. This condition wherein the artery is narrowed is known generally as stenosis.
Various therapies have been considered and developed for the treatment of obstructive vascular disease. One treatment is coronary artery bypass graft surgery. Bypass surgery, however, has the disadvantage that it is extremely invasive and traumatic to the patient. Accordingly, less invasive and less traumatic alternative therapies to bypass surgery are desired.
Several less invasive alternatives to bypass surgery have been developed that rely upon intravascular catheterization. Intravascular catheterization therapies involve the positioning of an elongate tubular catheter incorporating a therapeutic implement via a blood vessel to the site of the vascular obstruction to treat it. One such intravascular procedure is angioplasty. Angioplasty is a procedure in which an inflatable balloon is positioned on the inside of the artery at the site of the lesion and expanded in order to compress the materials at the lesion and thus open the restricted area in the artery. In this procedure, a balloon is attached to the distal end of a small diameter flexible catheter which includes a means for inflating the balloon from the proximal end of the catheter. The catheter is maneuvered through the patient's vessels to the site of the lesion with the balloon in uninflated form. When the uninflated balloon is properly positioned at the lesion, the balloon is then inflated to dilate the restricted area.
Although angioplasty is presently the most well developed and widely used intravascular therapeutic procedure, other intravascular catheterization therapies, such as atherectomy and laser irradiation, have also been considered and developed to a stage of at least limited success. Other therapeutic approaches in addition to these have also been considered and/or developed. Although existing therapies have proven to provide generally good results in many cases of obstructive vascular disease, no one therapy has yet proven to be successful for all cases of vascular disease. Moreover, with existing therapies for obstructive vascular disease, restenosis is observed in a significant percentage of cases following the intravascular procedure. Accordingly, there still is a need for a new therapy for treatment of obstructive vascular diseases.
One therapeutic approach that has been considered for treatment of obstructive vascular disease is the application of ultrasonic mechanical energy to the vascular obstruction. Ultrasound apparatuses and methods have been utilized for the removal or break up of undesired material in body locations other than blood vessels. For example, ultrasonic therapies have been utilized to remove kidney or gall stones and have been applied as well to other undesired materials, such as malignancies. In those therapeutic methods in which ultrasound has been successfully used to remove unwanted material from the body, the material to be removed has been in a location of the body at which a suitable methodology for delivery of the ultrasonic energy to the material could be utilized. One example of such an apparatus is a cell disrupter. A cell disrupter has a mechanical horn that is vibrated at a high natural frequency (e.g. 10-30 kilohertz) to direct ultrasonic energy to undesired cell groups or chemical groups in the body through a medium such as a biological fluid or chemical solution. The delivery of ultrasonic energy to the undesired cell or chemical group operates to break up the group.
Ultrasonic therapeutic methods have been considered for the break up and/or removal of undesired material or occlusions in blood vessels of the body. The use of ultrasonic energy to break up undesired material in the vascular system is promising because of the apparent selectivity in breakdown of undesired obstructive material compared to surrounding healthy tissue upon delivery of energy. Directed ultrasonic mechanical energy appears to selectively break down undesired material in a vascular region, such as plaque or thrombus, while causing no apparent damage to surrounding healthy vessel segments. However, despite the appeal of ultrasonic energy as a therapy for obstructive vascular diseases, it has so far not been successfully used for obstructive vascular diseases. One of the problems associated with the use of ultrasonic therapeutic techniques in the vascular system has been how to deliver the energy to blood vessel sites, especially vessel sites that are deep within the body.
At the present time, distal vessel sites, such as the coronary arteries in which stenosis commonly occurs, are routinely accessed by small diameter guide wires or catheters from remote locations such as the femoral artery for diagnostic and therapeutic procedures, such as angiographies, balloon angioplasties, and atherectomies. Further, physicians and clinicians who practice in this specialty have developed familiarity and skills as well as numerous accessories to assist in cardiovascular catheter and guide wire placement. Accordingly, it would be advantageous to utilize catheters and/or wires for ultrasonic energy delivery to a distal vessel location. However, using catheters and/or guide wires for the delivery of ultrasonic energy has several technical difficulties which have so far presented significant obstacles to the development of this therapy. Guide wires for use in positioning in the coronary tract may have a diameter on the order of 0.010 to 0.018 inches and a length of at least approximately 175 cm. Catheters and guide wires are designed to be flexible longitudinally in order to traverse tortuous vessel paths. Thus, because catheters and wires are usually designed to be flexible, they are not well suited to convey mechanical energy. Accordingly, the very properties desired and necessary in guide wires or catheters in order to position them are the same properties that have made them unsuitable for transmitting ultrasonic energy.
One previously considered approach to conveying ultrasonic energy via a wire to a distal vessel location is to set up a harmonic wave in the wire. According to this approach, a solid wire, made of titanium for example, can be vibrated at its natural frequency (which is a function of its length). A significant problem associated with conveying ultrasonic energy by such a method is that it causes the entire wire to vibrate transversely as well. This transverse motion generates considerable friction which results in undesirable attenuation along the length of the wire thereby resulting in a substantial amount of heat in the vessel. This is an undesirable result that precludes operation for a sufficient period of time to be effective. Moreover, the harmonic wave set up in the wire attenuates quickly if the wire is maintained in a curved configuration which is typical for access to remote vessel locations. These drawbacks have prevented this approach from achieving practical application.
Another concern associated with using ultrasonic techniques in a patient's blood vessel relates to the break up of the undesired material. The break up of undesired materials in a person's body in other body locations, such as in the kidney or gall bladder, by ultrasonic techniques may not be of concern because the presence of smaller, broken-up particles of the undesired material in such locations present little or no serious problem. However in arterial sites, the break up of material may pose problems. Assuming that ultrasonic energy could be successfully applied to a blood vessel obstruction, it is a concern that particles of the broken up occlusion may be carried away to another blood vessel location and cause a restriction of blood flow there. Worse yet, particles of a broken up occlusion may become lodged in other locations causing clots. Prior methods for applying ultrasonic techniques to blood vessels have not addressed capture or removal of particulate from the blood vessel following treatment.
Therefore, it is an object of the present invention to provide an apparatus, system and method for recanalization of an occluded or partially occluded body vessel through the use of delivering mechanical energy to a vessel location.
It is another object of the present invention to provide an apparatus, system, and method for use with other therapeutic methods and apparatuses and which is adapted to provide for recanalization of an occluded or partially occluded vessel at least to a degree to facilitate use of the other therapeutic methods or apparatuses.
It is yet further object of the present invention to provide an apparatus, system, and method for delivering mechanical energy over an elongate wire to a vascular site.
It is still a further object of the present invention to provide an apparatus, system, and method for delivering mechanical energy over an elongate wire to a vascular site without the build up or generation of heat due to transverse wire motion.
It is yet still a further object of the present invention to provide an apparatus, system, and method for removal of undesired material from a arterial site in conjunction with the recanalization of the artery by the delivery of mechanical energy to the artery site.